1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium suitable to increase recording density, a manufacturing method thereof and a magnetic recording device.
2. Description of the Related Art
In a hard disk device being one of recording devices, recording density is on the logarithmic increase. In an aim of increasing recording density, studies on the perpendicular magnetic recording, which magnetizes in the perpendicular direction to the surface of a magnetic recording medium, show progresses, while a longitudinal recording, which magnetizes in the parallel direction with the surface of the magnetic recording medium, has been employed to this date.
As shown in FIG. 22, according to the perpendicular magnetic recording, information is recorded in a manner in which a recording layer of a perpendicular magnetic medium 105 is magnetized in accordance with magnetic field from a main magnetic pole 103 of a magnetic head. The magnetic head is also provided with a return yoke (auxiliary magnetic pole) 102 connected to the main magnetic pole, a coil 101 generating magnetic field, and a reproducing element 104 reading out information from the perpendicular recording medium.
As shown in FIG. 23, in a perpendicular magnetic recording medium, an adhesive layer 112, a soft magnetic underlayer 113, an intermediate layer 114, a granular layer (recording layer) 115, a cap layer 116, a protective layer 117, and a lubricant layer 118 are stacked on a glass substrate 111. In the perpendicular magnetic recording medium of the structure as described above, a recording magnetic field from a magnetic head is refluxed to obtain a favorable recording characteristic. Note that, in the perpendicular magnetic recording, demagnetizing field is generated from the surface of the recording medium. Therefore, a recording/reproducing characteristic varies depending on an initialized state. For example, as shown in FIG. 25, a curve (M-H curve) indicating a change in magnetization M when magnetic field H is applied from the direction perpendicular to the perpendicular magnetic recording medium goes upward almost vertically (broken line) when there is no influence of the demagnetizing field, while the curve slants when there is influence of the demagnetizing field (solid line). When the effect of the demagnetizing field as described above is considered, it is stable in view of energy when the magnetization is reversed little by little as compared with the case where the magnetization is constant, so that the perpendicular magnetic recording can be said to be suitable for high density recording.
In addition, in an aim of increasing recording density, studies on a recording medium called as a discrete track medium show progress as well. As shown in FIG. 26, in a conventional recording medium 121, a plurality of recording tracks 122 are arranged in a closely approaching manner to each other, and recorded portions 129 are formed in the recording tracks 122. However, as shown in FIG. 27, in the structure as described above, sometimes a writing running over the adjacent recording track 122 or a writing blotting out the adjacent track 122 is caused. As a result, information already recorded in the adjacent recording track 122 is sometimes erased.
As measures against the above-described situation, in the discrete track medium, a groove portion 123 is provided between the recording tracks 122 as shown in FIG. 28, or a magnetic portion 124 and a nonmagnetic portion 125 are provided as shown in FIGS. 29 to 31. In the example shown in FIG. 29, on the surface of the magnetic portion 124 being a base portion, a plurality of nonmagnetic portions 125 are formed to form the recording tracks 122 therebetween. In the example shown in FIG. 30, inside the magnetic portion 124 being a base portion, a plurality of nonmagnetic portions 125 are embedded to form the recording tracks 122 therebetween. In the example shown in FIG. 31, on the surface of the nonmagnetic portion 125 being a base portion, a plurality of magnetic portions 124 is formed to make the recording tracks 122 be the recording tracks 122 themselves.
In the discrete track medium shown in FIG. 28, recorded portions 129 are formed as shown in FIG. 32, and in the discrete track medium shown in FIG. 29, recorded portions 129 are formed as shown in FIG. 33. At this time, since the groove portion 123 or the nonmagnetic portion 125 exists between the recording tracks 122, the erase (side erases) of the information in the adjacent recording track 122 can be prevented even if the blotting out or running over of a writing is caused. The same is also applicable to the discrete track shown in FIG. 30 or 31.
As described above, in order to increase the recording density, it is effective to adopt the perpendicular magnetic recording and the discrete track medium.
However, under the present circumstances, these technologies are impossible to be combined. When an initialization process called an AC erase process adopted in the perpendicular magnetic recording is performed to the discrete track medium, an appropriate reproduction becomes difficult. This is a fact that the present inventor has found first.
Related arts are disclosed in Japanese Patent Application Laid-Open No. 2006-31846 and Japanese Patent Application Laid-Open No. 2006-48751.